1. Field of the Invention
The invention relates to a twin spool turbine engine with power take-off means on the low-pressure and high-pressure rotors, to a power take-off module for the turbine engine and to a method for assembling the turbine engine.
2. Discussion of Background
Some of the power generated by an aeronautical turbine engine is used to power various components, both of the turbine engine and also of the aircraft to the propulsion of which the turbine engine contributes.
Some of this power is actually tapped off the high-pressure (HP) compressor, the compressed air of which is used in particular to pressurize and air-condition the cabin of the aircraft, or for de-icing purposes. Some more of this power is tapped mechanically off the shaft of the HP stage of the turbine engine, to drive the input shaft of an accessory gearbox positioned on a casing of the turbine engine. This input shaft is rotationally driven by a transmission shaft running along a structural arm of the casing and itself driven by a pinion secured to the HP shaft.
The accessory gearbox, well known to those skilled in the art by the abbreviation AGB, comprises various machines or accessories, for example a generator, a starter, an alternator, hydraulic fuel or oil pumps, etc. These various accessories are mechanically driven by the HP shaft.
The current trend is to increase, on the one hand, the tapping of mechanical power because of the increasing role played by electrical means which are reputed to be more flexible in their use.
However, tapping off excessive amounts of mechanical power has a negative effect on the operation of the HP spool because it is liable to cause compressor surge, particularly when the engine is running at low speed.
The teachings of the prior art are to tap some of the mechanical power from the low-pressure (LP) spool. Various solutions have been imagined. Document FR 2 606 077 proposes to connect the rotors of the turbine engine directly to the two inputs of a differential positioned near them. Such an arrangement is not, however, always possible because of the space that this arrangement requires within the heart of the turbine engine. Document GB 973 388 describes, for an industrial turbine, driving the accessory gearbox, situated on the exterior casing of the turbine, using power take-offs from the HP shaft and the LP shaft: however, the power take-offs from each of the shafts are connected to the accessory gearbox by bulky gear sets. Such cannot be done in a modern turbine engine in which these gear sets have to pass through the structural arms of the casing.
The applicant company has filed the French Patent Application No. FR 03 14 429 regarding a twin spool turbine engine, the accessory gearbox of which is driven by the LP and HP shafts, which are connected to transmission shafts, each passing through one structural arm and which are connected to the two inputs of a differential connected at output to the drive shaft of the accessory gearbox. While such a solution is advantageous in numerous respects, it is, however, sometimes necessary not to clutter two structural arms, this being so as to leave the greatest possible amount of space for running the auxiliaries through. The auxiliaries are fluid-carrying pipework or trunking for electrical cables carrying power or information (speed sensors for example).
Document U.S. Pat. No 4,776,163 describes a jet engine in which the HP and LP shafts can alternately drive the accessory gearbox, to which they are connected by coaxial transmission shafts. Because they are coaxial, these shafts can run along a common structural arm. However, as can be seen from the FIGURE in that document, the power take-off from the rotors at the end of the shafts is very bulky and requires a significant amount of space over a broad region of the shafts.